Contemplate the scenario where a K8 managed application becomes
not_installable after being installable.

Use update term instead of update in the clusters managed app
implementation in order to make the implementation and UI
language more consistent.

- Vue confirmation modal implementation
- CSS tweaks for modal default height

- Separate cluster application UI state from server-side app status
- Use a state machine to determine cluster application next state
- Instead of using two variables to keep track of when an app
is installing or updating, just use the app status property and control
server-side and user events using the FSM service.

Added the functionality to edit the Knative domain

Includes juptyer hostname in the post request
Adds tests

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>